Process for producing cellulose esters



Patented May 17, 1932 STATES PATENT oFFicE GEORGES HEBERLEIN AND ALBERTBODMER, OF WATTWIL, SWITZERLAND, ASSIGNOBS TO HEBERLEIN & 00., A G., F'WA'I'TWIL, SWITZERLAND, A CORPORATION OF SWITZ PROCESS FOR PRODUCINGGELLULOSE ESTEIRS No Drawing. Application filed August 25, 1928, SerialNo. 302,138, and in Germany September 30, 1927.

This invention relates to a process for producing cellulose esters.

The object of the invention is to effect esterification of the cellulosein a more expeditious and efiective manner.

It has been known that the reaction in the esterification of celluloseis a slow one; and in order to improve same in the case of acetylcellulose it has been proposed to first convert the cellulose by apretreatment into hydro-cellulose by treating the cellulose with verydilute sulphuric acid (3% sulphuric acid) and then drying and heatingthe cellulose. The resulting hydro-cellulose was then acetylized bytreating it with acetic anhydride in the presence of sulphuric acid.According to said known treatment the sulphuric acid was too weak tobring about a swelling action of the cellulose fibre, i. e., too

weak to act as a swelling means for the fibres; but the heating of thefibres when dry was required to convert the cellulose intohydrocellulose, i. e., to effect a hydrolyzation of the cellulose.

undesirable as it changes the cellulose structurally in a manner toeffect a certain destruction or disintegration in the cellulose which isundesirable in the treatment, since it results in a substantiallyuseless or a very 3o inferior product for the production of artificialsilk, films, etc. This process was therefore given up.

We have discovered that the esterification of cellulose can beaccomplished in a rapid and uniform manner if instead of hydrolyzing thecellulose fibres (such for example as cotton fibres) as heretoforeproposed, the fibres are pretreated so as to cause them to swell, andwhile in the swollen state they are subjected to the action of thereagent or reagents. The object of the swelling action is to bring abouta physical change in the fibres such as to render the material thereofmore readily accessible to the reagent. .The swelling should be carriedout preferably without hydrolyzation, and in any event withoutsubstantial hydrolyzation, it being desirable where an acid swellingagent is used for the pretreatment, to effect the swelling in suchmanner as to avoid, if possible, any hy- This. hydrolyzation, however,is.

drolyzation of the fibres. It is also important that the swollencondition of the fibres is maintained until the esterifying reagent isapplied, and that undesirable coagulation of the swollen fibres shouldnot take place before the esterifying reagent is applied.

Further objects and advantages of the invention will more fully appearfrom the following description of some preferred methods of carrying outthe invention.

As suitable swelling agents there may be used such of the known or usualswelling agents as are of an acid character or of a socalled neutralcharacter; as distinguished from those of an alkaline character. Forexample there may be used concentrated mineral acids such as sulphuric,phosphoric, nitric, hydrochloric or the like, either separately or inmixtures; also salts having swelling properties, such for example aszinc chloride, calcium thiocyanate, etc. While these salts are not in astrict technical sense exactly neutral, yet for the purpose of thisinvention they may be regarded as neutral in comparison to the acidswelling agents and to the 7 alkaline swelling agents such as -causticand Schweitzers solution. Alkaline swelling agents are to be avoidedbecause if they are used, then when the swollen fibres are treated withthe esterifying mixture, which is acid, 30 there will take place amomentary coagulation, and hence a destruction of the desired swollenstate of the fibres. Alkaline swelling agents are therefore not usableunless some means should be provided whereby this re- 5 sultingundesirable coagulation could be overcome.

The character and strengths of the various swelling agents, the durationof treatment of various kinds of cellulosic fibres thereby, etc., toeffect swelling without detri mental efi'ect to the particular fibrestreated, are now all well understood and need not, be detailed. Thoseskilled in the art also now known that when acid swelling agents areused on cellulosic fibres, that if the swelling action is'permitted tocontinue after the swelling of the fibres has taken eflect, theundesirable hydrolyzation may take place; and care should be taken tostop the action of the acid swelling agent in time to avoid, ifpossible, any hydrolyzation of the fibres.

As is known, the strength of the agent, the character of the fibres, andother factors and conditions will come into consideration in determiningthe permissible length of the swelling treatment in each case, so thatno' go this mixture upon the fibres, the fibres after water or organicsolvents having been swollen can be washed out so that the residue ofswelling agent is reduced to an uninJurious quantity or is removedaltogether. The swelling agent can be washed out by as for instancealcohol, glacial acetic acid, or acetone. The washing means can beremoved in any suitable manner as for example by squeezing out orcentrifuging the fibres, etc.; but drying must be avoided.

upon by the reagents.

The esterification of the swollen fibres is carried out in known manneras for example with concentrated organic acid, acid anhydrides, acidchlorides or reagents having a similar action, and if necessary ordesirable utilizing therewith a catalizer. After the reaction has takenplace the mass is poured P into water or into a precipitating bath andthe converted cellulose is isolated. The primary esters that are formedmay also be converted into the more readily soluble secondary productsin well known manner by means of partial saponification ortransformation. The products that are obtained may be dissolved in theusual solvents, for example, acetone, chloroform, pyridin, etc.; and outof this solution artificial silk, films or lacquers can be produced. Theproduction of moulded structures may also be effected by means of directcoagulation of the said mass.

As the materials to be treated, one may use any suitable cellulosicmaterial or cellulosiccontaining substance capable of being acted Forexample, cellulosic fibres such as cotton may be used or othercellulosic material preferably in the form of finely divided fibrousmaterial; but moderately reduced material may also be utilized such aswood splinters or the like, capable of being acted upon by the reagents;also paper pulp may be used.

Examples 1. Previously bleached cotton waste is introduced intosulphuric acid of 62% strength in the cold state, and is left thereinfor several minutes until swollen. The sulphuric acid is then drawn offand the surplus acid is pressed out, the remaining substance (swollenfibres) being then introduced into the esterifying mixture which mayconsist of 6 parts of acetic acid anhydride and 6 parts of glacialacetic acid, these parts being by weight with relation to the unit ofweight of the dry cellulosic fibre. The temperature is maintained belowabout 40 C. by means of cooling. The reaction sets in very rapidly andis concluded in a quarter of an hour, whereupon the product can beisolated by precipitation in water.

2. Cleaned or purified loose cotton is allowed to swell for a quarter ofan hour in nitric acid of 7 0% strength, whereupon most of the acid isremoved by pressing. The residue of the nitric acid is then removed fromthe fibres by washing by means of glacial acetic acid,

whereupon the mass is pressed out again. Thereupon the esterifyingmixture is caused to act on the mass while in the swollen state. Thismixture may consist of 4: parts of acetic acid anhydride, 4: parts ofglacial acetic acid and 0.15 parts of concentrated sulphuric acid, theseparts being by weight with relation to the unit of weight of the drycotton. The temperature is kept below about 30 C. and the reaction iscompleted in two hours. The esterify cellulose is now removed byprecipitation in the usual manner.

As heretofore stated, coagulation or drying of the swollen goods shouldbe avoided rior to the esterifying reaction and care should be taken toavoid detrimental hydrolyzation.

By the use of the term neutral character as used in the specificationand claims to characterize the swelling agents, we wish to be understoodas using the term in its broader sense, i. e., as meaning swellingagents which are substantially neutral in character, as contrasted withthe decided acid or sour character of the acid swelling agents and ascontrasted with the decided alkaline character of what are generallyknown as alkaline swelling agents, such for example as caustic acid andSchweitzers solution. Also, by the term suitable swelling agent as usedin the claims, we wish to be understood as including swelling agents ofacid and neutral character as herein mentioned, and also any otherswelling agents of an acid or neutral character having similar actionfor the purpose.

Thus while we have described our improvements in detail and with respectto certain preferred forms, we do not desire to be limited to suchdetails or forms since, as will be understood by those skilled in theart after understanding our invention, many changes and modificationsmay be made and the invention embodied in widely different forms whichcomprises producing a swelling action tion, treating said material witha reagent to esterify it.

Having thus described our invention, what we claim as new anddesire tosecure by Let- 5 or more of the appended claims.

ters Patent, is:

1. Pprocess of producing cellulose esters in the cellulosewithoutsubstantial production of hydrocellulose, and while it is in theswollen condition and not alkaline in reaction, treating said cellulosewith a reagent to 2. Process of producing cellulose esters without;substantial production of hydro! cellulose, and while it is in swollencondition, treating said material with a reagent to 10. Process ofproducing acetyl cellulose ,which comprises treating cellulose with astrong mineral acid to swell the material without substantial"production of hydrocellulose, and while \it is in swollen condi-'acetylize it. I I

In testimony whereof we have signed our names to this specification.

GEORGES HEBERLEIN} ALBERT BODMER.

which comprises swelling the cellulose without substantial production ofhydrocellulose by treating it 'witha non-alkaline swelling agent andwhile-swollen treating said cellu lose with a,reagent to esterify it.

3. Process of producing cellulose esters which comprises treatingthecellulose without substantial production of hydrocellulose with anon-alkaline swelling agent until the material is swollen, removing theexcess swelling agent from the ccellulose and thereupon treating saidswollen material with a reagent to esteri'fy it.

' 4. Process of producing cellulose esters 4 which comprises treatingthe cellulose without substantial production of hydrocellulose with aswelling agent to swell the same a d thereupon treating theswollencellulose with 5 a reagent to esterify it. o a

5. Process of producing-cellulose esters which comprises treating thecellulose without substantial production of hydrocellulose with a,swelling agent to swell the same, removing the excess swelling agentfrom the cellulose and theteupon treatingthe swollen cellulose with areagent'to esterify it.

6. Process of producing cellulose esters which'comprises treating thecellulose without substantial production of hydrocellulose with anon-alkaline swelling agent until the material is swollen, washing theswollen celluloseland thereupon treating said cellulose with a reagentto esterify it.

7. Process of producing acetyl cellulose 4 esters which comprisestreating the cellulose without substantial production of hydrocellulosewith a swelling agent to swell the same,

removing the excess swelling $5 cellulose, then washing'the cellulose toremovean additional amount of the swelling agent from tha agenttherefrom, and thereupon treating the swollen material with a reagent toacetylize it.

8. As a product'of" manufacture, a cellulose ester made according to-theprocess of claim 1. v

9. Process of producing acyl cellulose which comprises treatingcellulose with a strong mineral acid to swell the material I CERTIFICATE01 commtmon :mm No. 1,858,993 ",Ma u', 1932. f

GEORGES mum ET AL.

' It ilsherebg cettified that error appears in the minted speciiicatibnat the above numbened patent requiring correction as follnwszL Page 1,line 95, for "known? read know; page Byline 51, claim 7, strike out theword "esters";' and that the said Letters Patent should be read withthese cot ection therein that the same may conform, to" the record ofthe case in the Patent Offine'. Signed and sealed this 12th day of July,B 1932.

' Mr'J. Moore, Seal Acting Commissioner of'Patents,

